Aim To investigate the protective effects of icariin(ICA) on oxidative injury of human umbilical vascular endothelial cells (HUVEC) caused by H2 02 and analysis action machenisms of ICA.Methods HUVEC were cultured in DMEM medium with 10% fetal bovine serum and 1% antibiotic mixture comprising penicillin and streptomycin, at 37℃ with 5% CO2 in vitro.The model of oxidative injury was established by H2O2 (750 μmol ·L 1).The cells were divided into six groups: control group, H2O2 group, H2O2 +ICA(10s, 107, 106 mol ·L1) group and H2O2 + DMSO (solvent) ; HUVEC were treated with different concentration ICA according to grouos before 12h H2O2 treatment and cultured for 12, 24 and 36h respectively, the cell vitality (OD value) and the level of ROS was measured by MTT and ELISA.The apoptosis and death of HUVEC were detected using Annexin VFITC/PI kit.Real Time RTPCR was used to detect Bcl2 and Bax mRNA expression in the HUVEC.Results Compared with control group, cell vitality siguificantly declined (P <0.01) , the level of ROS and the number of apoptotic HUVEC notably increased (P <0.01) in H2O2 group.Compared with H2O2 group, ICA treatment could increase HUVEC vitality and reduce level of ROS (P < 0.01 or P < 0.05) with manners of timedependence and dosedependence,ICA treatment could decrease the apoptosis and death rate of HUVEC (P < 0.01).ICA treatment could also downregalate the expression of Bax mRNA (P < 0.05) and upregulate the expression of Bcl2 (P<0.05).Conclusion The ICA can alleviate the oxidative injury of HUVEC induced by H2O2 treatment, The action mechanisms of ICA may, at least partly, be related to inhibit HUVEC apoptosis caused by H2O2 treatment through upregulation of expression of Bcl2 and downregulation of expression of Bax mRNA.